Lipids

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Chemistry 203
Chapter 19 Lipids
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Lipids

• - Family of bimolecules.

- They are not defined by a particular
functional group, thus they have a variety of
structures and functions.
- They are soluble in organic solvents but not in
water (nonpolar).
- They contain many nonpolar CC and CH bonds
and few polar bonds resulting in their water
insolubility.
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Lipids
1. Store energy fat cells
2. Chemical messengers find in nerve fibers and
hormones.
3. Parts of membranes insoluble in water
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Lipids
1. Simple lipids (Waxes, Fats Oils)
2. Complex lipids (Glycerophospholipids)
3. Steroid (Cholesterol steroid hormones)
4. Eicosanoids
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Lipids
Lipids can be categorized as

1. Hydrolyzable lipids can be converted into small
   molecules by aqueous hydrolysis.

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Lipids
Lipids can be categorized as

1. Nonhydrolyzable lipids cannot be cleaved into
   smaller molecules by aqueous hydrolysis.

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Hydrolysis
Most hydrolyzable lipids contain an ester.
Hydrolysis reaction with water. (breaking a
bond and adding the elements of water)
Heat
H or enzyme
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Fatty acids
Hydrolyzable lipids are derived from fatty acids.

• Fatty acids are
• Long-chain unbranched carbon attached to a
  carboxyl group (-COOH).
• Typically 12-20 carbon atoms.
• They have an even number of C atoms.
• Insoluble in water.

Cis
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Fatty acids
CH3(CH2)14COOH (palmitic acid)
polar portion hydrophillic
nonpolar portion hydrophobic
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Saturated and unsaturated Fatty acids
Saturated fatty acids have no double bonds in
their long hydrocarbon chains.
Stearic acid CH3(CH2)16COOH
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Saturated and unsaturated Fatty acids
Unsaturated fatty acids have 1 or more double
bonds (generally cis) in their long hydrocarbon
chains.
Oleic acid CH3(CH2)7CHCH(CH2)7COOH
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Fatty acids

• The human body is capable of synthesizing most
  fatty acids from
• carbohydrates or other fatty acids.
• Humans do not synthesize sufficient amounts of
  fatty acids that
• have more than one double bond.
• More than one double bond fatty acids are called
  essential fatty acids and they must be provided
  by the diet.

Linoleic acid linolenic acid
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Essential Fatty acids
Omega-n acids
n the position of the first double bond
Linoleic acid is called an omega-6 acid, because
of the position of the first CC in the nonpolar
chain.
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Essential Fatty acids
Linolenic acid is called an omega-3 acid, because
of the position of the first CC in the nonpolar
chain.
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Waxes
Wax is an ester of saturated fatty acid and long
chain alcohol.
Acid
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Waxes
For example, shown below is the formation of
spermaceti wax, isolated from the heads of sperm
whales.
Acid
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Waxes

• Because of their long nonpolar C chains, waxes
  are very hydrophobic.

O
Beeswax (myricyl palmitate)
CH3(CH2)14
C
O(CH2)29CH3
hydrophobic region
hydrophobic region
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Carnauba
Beeswax
Coating
Jojoba
Lanolin from wool
lotions
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Waxes
Hydrolysis reaction like other esters, waxes are
hydrolyzed.
Heat
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Triacylglycerols (Triglycerides)

• Triacylglycerols are
• Fats and oils (are stored in the body).
• Triesters of glycerol.
• Produced by Fischer esterification.
• Formed when the hydroxyl groups of glycerol react
  with the carboxyl groups of fatty acids.

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Esterification
glycerol three fatty acids
triacylglycerol
3H2O
Acid
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Triacylglycerols (Triglycerides)
Glycerol
Produced by esterification of glycerol (a
trihydroxyl alcohol).
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Triacylglycerols (Triglycerides)
Simple triacylglycerols have three identical
fatty acid side chains.
Mixed triacylglycerols have two or three
different fatty acids.
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Triacylglycerols (Triglycerides)
Saturated triacylglycerols contain only saturated
fatty acids.
Monounsaturated triacylglycerols have 1 CC bond.
Polyunsaturated triacylglycerols have many CC
bonds.
Increasing the number of double bonds in the
fatty acid chain decreases the melting point of
the triacylglycerol.
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Triacylglycerols (Triglycerides)
Fat is a triacylglycerol that is solid at room
temperature. Made by more saturated fatty acids
(Saturated triacylglycerols). Meat, milk, butter
and cheese (animal sources).
Oil is a triacylglycerol that is liquid at room
temperature. Made by more unsaturated fatty
acids (Unsaturated triacylglycerols). Corn,
cotton seed, safflower and sunflower (plant
sources).
Both are colorless, odorless, and tasteless.
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Fat Health
- Fats are used to build cell membranes, insulate
the body, and store energy for later use.
- It is recommended that no more than 20-35 of a
persons caloric intake should come from lipids.
- A high intake of saturated triacylglycerols is
linked to heart disease.
- Saturated fats stimulate cholesterol synthesis
in the liver, which can lead to cholesterol
plaques building up inside arteries.
- The result is high blood pressure, heart
attack, and even stroke.
- Unlike other vegetable oils, oils from palm and
coconut trees are very high in saturated fats.
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Fat Health
- Unsaturated triacylglycerols (omega-3 fatty
acids from fish) lower the risk of heart disease
by decreasing the level of cholesterol in the
blood.
- However, if the double bond of the unsaturated
triacylglycerol is trans, the beneficial effect
is lost.
- Trans fats, which are primarily synthesized
instead of naturally occurring, act like
saturated fats and increase the cholesterol
levels in the blood.
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1- Hydrogenation

• Hydrogen adds to the double bonds of unsaturated
  fats (using transition
• metal catalyst such as Ni).
• Melting point is increased.
• - Liquid oils are converted to semi-solid fats.

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1- Hydrogenation
Ni
3H2 glyceryl
Trioleate (triolein)
glyceryl tristearate
(tristearin)
_
_
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2- Hydrolysis
Triacylglycerols are hydrolysis (split by water)
in the presence of strong acid or lipase
(digestive enzyme).

3H2O
H
3H
O
H

H or Lipase
H
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Metabolism of tricaylglycerols
- Humans store energy as triacylglycerols in
adipose cells below the surface of the skin, in
the breast area, and surrounding internal organs.
- The number of adipose cells is constant weight
gained or lost causes them to swell or shrink,
but not decrease or increase in number.
- To metabolize triacylglycerols for energy, the
esters are hydrolyzed by enzymes called lipases.
- Complete metabolism of a triacylglycerol yields
CO2, H2O, and a great deal of energy.
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3- Saponification (Basic Hydrolysis)

• - Is the process of forming soaps (salts of
  fatty acids).
• - Is the reaction of a fat with a strong base
  (NaOH).
• - Splits triacylglycerols into glycerol and the
  salts of fatty acids.
• - With KOH or the oils that are polyunsaturated
  gives softer soaps (liquid soaps).
• - Soaps are typically made from lard (from hogs),
  tallow (from cows or sheep), coconut oil, or palm
  oil.
• - All soaps work in the same way, but have
  different properties depending on the lipid
  source, length of C chain, and degree of
  unsaturation.

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3- Saponification (Basic Hydrolysis)

3NaOH
H
Heat
H

Na-O
3
soap
Salt of fatty acid
H
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Soaps
Hydrophobic part nonpolar
Hydrophilic part polar (remains in contact with
environment)
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Soaps
When soap is mixed with dirt (grease, oil, and
), soap micelles dissolve these nonpolar,
water-insoluble molecules.
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phospholipids
Phospholipids are lipids that contain a P atom.
Two common types
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phospholipids
1. Phosphoacylglycerols
They are the main component of most cell
membranes.
Structurally, they resemble a triacylglycerol,
except the third fatty acid has been replaced
with a phosphodiester bonded to an alcohol.
Fatty acid
Fatty acid
Amino alcohol
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phospholipids
1. Phosphoacylglycerols
There are two types of phosphoacylglycerols
Ethanolamine
Choline
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phospholipids
2. Sphingomyelins They differ in two ways
1. They do not contain a glycerol backbone, they
have a sphingosine backbone instead.
sphingosine
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phospholipids
2. Sphingomyelins
The myelin sheath, the coating that surrounds
nerve cells, is rich in sphingomyelins.
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phosphoacylglycerols
Nonpolar
O R
Polar
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Cell Membrane
Semipermeable selected nutrients can enter and
waste products can leave.
Fluid mosaic model
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Cell Membrane
- Peripheral proteins are embedded within the
membrane and extend outward on one side only.
- Integral proteins extend through the entire
bilayer.
- Sometimes carbohydrates are attached to the
exterior of the cell forming glycolipids and
glycoproteins.
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Transport Across a Cell Membrane
Simple Diffusion Small molecules like O2 and CO2
can diffuse through the cell membrane, traveling
from higher to lower concentration.
Facilitated Transport Larger polar molecules
(glucose) and ions (Cl- and HCO3-) travel through
integral protein channels.
Active Transport Other ions, Na, K, and Ca2,
move against the concentration gradient this
required energy input.
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Steroids

• Steroids have
• A steroid nucleus which is
• 4 carbon rings.
• Attached groups that make the different types of
  compounds.
• No fatty acids.

(steroid nucleus)
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Cholesterol

• Cholesterol
• Is the most abundant steroid in the body.
• Insoluble in water (need a water soluble
  carrier).
• Has methyl CH3- groups, alkyl chain, and -OH
  attached to the steroid nucleus.

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Cholesterol

• Cholesterol
• Is obtained from meats, milk, and eggs.
• Is synthesized in the liver from fats,
  carbohydrates and proteins.
• Is needed for cell membranes, brain and nerve
  tissue, steroid hormones, and Vitamin D.
• Clogs arteries when high levels form plaque
  (because it is insoluble in blood).
• No cholesterol in vegetable and plants.

At artery clogged by cholesterol plaque
Gallstones form in gallbladder
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Lipoproteins
Water-soluble form of lipids (soluble in blood)
Spherical particles Polar surface and nonpolar
inner
Transporting lipids through the bloodstream to
tissues where they are stored, Used for energy,
or to make hormones.
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Lipoproteins
VLDL very-low-density lipoprotein
Triglycerides and Cholesterol
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Steroid Hormones
A hormone is a molecule that is synthesized in
one part of an organism, which then elicits a
response at a different site.
Two types of steroids hormones
1. Sex hormones 2. Adrenal Cortical Steroids
Estrogens progestins in females
Androgens in males
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Sex Hormones
Estrogens (Female Sex Hormones)
The estrogens estradiol and estrone control
development of secondary sex characteristics,
regulate the menstrual cycle, and are made in the
ovaries.
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Sex Hormones
Progestins (Female Sex Hormones)
The progestin progesterone is called the
pregnancy hormone it is responsible for the
preparation of the uterus for implantation of a
fertilized egg.
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Sex Hormones
Androgens (Male Sex Hormones)
Testosterone and Androsterone are androgens made
in the testes.
They control the development of secondary sex
characteristics in males.
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Sex Hormones
- Synthetic androgen analogues, called anabolic
steroids, promote muscle growth.
- They have the same effect as testosterone, but
are more stable, so they are not metabolized as
quickly.
- They have come to be used by athletes and body
builders, but are not permitted in competitive
sports.
- Prolonged use of anabolic steroids can cause
physical and psychological problems.
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Sex Hormones
Some examples of anabolic steroids
(THG or the Clear)
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Adrenal Cortical Steroids
Aldosterone regulates blood pressure and volume
by controlling the concentration of Na and K in
body fluids.
Cortisone and cortisol serve as anti-inflammatory
agents, which also regulate carbohydrate
metabolism.
aldosterone
cortisone
cortisol
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Adrenal Cortical Steroids
Cortisone are used to suppress organ rejection
after transplant surgery and to treat many
allergic and autoimmune disorders.
Prolonged use of these steroids can have
undesired side effects, including bone loss and
high blood pressure.
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Vitamins
They are organic compounds required in small
quantities for normal metabolism.
They must be obtained from the diet (our cells
cannot synthesize them).
Vitamins are either water soluble or fat soluble.
The four fat-soluble vitamins (A, D, E, and K)
are lipids and nonpolar.
They are found in fruits, vegetables, fish,
liver, and dairy products.
Excess vitamins are stored in adipose cells to be
used when needed.
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Vitamins
Vitamin A
It is found in liver, fish, and dairy products,
and is made from ß-carotene (the orange pigment
in carrots).
It is needed for vision and for healthy mucous
membranes.
Vitamin A deficiency causes night blindness and
dry eyes and skin.
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Vitamins
Vitamin D
Vitamin D can be synthesized from cholesterol.
It can be obtained in the diet from many foods,
especially milk, and helps regulate Ca and P
metabolism.
A deficiency of vitamin D causes rickets (bone
malformation).
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Vitamins
Vitamin E
Vitamin E is an antioxidant, protecting
unsaturated side chains in fatty acids from
unwanted oxidation.
Deficiency of vitamin E causes numerous
neurological problems, although it is rare.
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Vitamins
Vitamin K
Vitamin K regulates the synthesis of clotting
proteins (prothrombin), and deficiency of this
leads to excessive or fatal bleeding.
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Eicosanoids
Prostaglandins and Leukotrienes are two types of
eicosanoids (20 C atoms derived from the fatty
acids).
- All eicosanoids are very potent compounds,
which are not stored in cells, but rather
synthesized in response to external stimulus.
- Unlike hormones they are local mediators,
performing their function in the environment in
which they are synthesized.
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Prostaglandins
Prostaglandins are carboxylic acids that contain
a five-membered ring and have a wide range of
biological activities.
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Prostaglandins
Prostaglandins are responsible for inflammation.
- Aspirin and ibuprofen relieve pain and
inflammation by blocking the synthesis of these
molecules.
- Prostaglandins also decrease gastric
secretions, inhibit blood platelet aggregation,
stimulate uterine contractions, and relax smooth
muscles.
- There are two different cylcooxygenase enzymes
responsible for prostaglandin synthesis called
COX-1 and COX-2.
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Prostaglandins
COX-1 is involved in the usual production of
prostaglandins.
COX-2 is responsible for additional
prostaglandins in inflammatory diseases like
arthritis.
- Nonsteroidal anti-inflammatory drugs (NSAIDs)
like aspirin and ibuprofen inactivate both COX-1
and -2, but increase risk for stomach ulcer
formation.
- Drugs sold as Vioxx, Bextra, and Celebrex block
only the COX-2 enzyme without affecting gastric
secretions.
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Leukotrienes
Asthma is characterized by chronic inflammation,
so inhaled steroids to reduce this inflammation
are commonly used.
Leukotrienes are molecules that contribute to the
asthmatic response by constricting smooth muscle
of the lung.
New asthma drugs act by blocking the synthesis of
leukotriene C4, which treat the disease instead
of just the inflammation symptoms.